Z. Ogumi

Anodic Oxidation of Polyhydric Alcohols on a Pt Electrode in Alkaline Solution

The electrochemical oxidation of various polyhydric alcohols, ethylene glycol, glycerol, meso-erythoritol, and xylitol, on a platinum electrode was investigated systemematically in acidic H2SO4, and in alkaline KOH and K2CO3 solutions to evaluate the potential of these polyhydric alcohols as fuels in micro-fuel cells for portable electronic devices. All polyhydric alcohols tested in the present study showed high reactivities in both alkaline solutions. Ethylene glycol showed the highest reactivity. Although the reactivity of ethylene glycol was lower in K2CO3 than in KOH, the carbonate solution is a potential candidate as an electrolyte solution due to its resistance to solution carbonation. Furthermore, ethylene glycol showed much less significant electrode poisoning by adsorbed CO upon oxidation in alkaline solution.

Structure and electrochemical behaviors of LixCoO2 (x>1) treated under high oxygen pressure

Abstract The electrochemical behavior of LixCoO2 (x>1.0) and its high pressure oxygen-treated samples were examined as cathode of lithium ion battery. LixCoO2 was prepared at nominal compositions of Li/Co=1.02, 1.05, 1.10, 1.15, 1.20, 1.25, and 1.30. The practical compositions and cobalt valences were analyzed by ICP and iodometric titration technique. X-ray diffraction patterns show that the lattice gradually contracts with increasing Li/Co ratio. The lattice contraction stops at Li/Co=1.15, which corresponds to the solid solution limit. The high oxygen pressure treatment reduced the number of oxygen defects and enlarged the interlayer distance. The electrochemical behavior of oxygen-treated samples show better cycling efficiency and less irreversible capacities. The reversible capacities show clear dependence on Li/Co ratio that the highest capacity of 140 mA h g−1 was obtained when Li/Co=1.10 and beyond that value it decreased linearly with Li/Co ratio.

Concentration determination of oxygen nanobubbles in electrolyzed water.

Water electrolysis is well known to produce solutions supersaturated with oxygen. The oxygen in electrolyzed solutions was analyzed with a dissolved oxygen meter and the Winkler method of chemical analysis. The concentration of oxygen measured with the dissolved oxygen meter agreed with that obtained using the Winkler method. However, measurements using a 10-fold dilution method showed a larger concentration of dissolved oxygen compared to the above methods. We developed a modified Winkler method to measure total oxygen concentration more accurately, which agreed with the results obtained from the 10-fold dilution experiment. The difference in measurements is due to the existence of oxygen nanobubbles, as confirmed by the observation of dynamic light scattering using a laser. Further analysis of the oxygen nanobubbles demonstrated that the stability of the nanobubbles was sufficient for chemical reaction and solvation to bulk solution.

Creation of nanospaces by intercalation of alkali metals into graphite in organic solutions

Abstract Co-intercalation of alkali metals (Li, Na, K, Rb and Cs) with various organic solvents has been utilized for introducing nanospaces in graphite. The co-intercalation has been conducted by a solution method. Resultant products were studied by X-ray diffraction. For solvents of cyclic ethers, co-intercalation is likely to occur for heavy alkali metals of Rb and Cs. For linear ethers with one oxygen atom, binary graphite intercalation compounds (GICs) were mainly obtained, irrespective of alkali metal species. For linear ethers with two oxygen atoms, light alkali metal, in particular, Li tends to give ternary Li–solvent–GICs. From these results, it is concluded that co-intercalation is mainly influenced by the interaction between alkali metals and solvents and by the size of solvated alkali metals.

Graphite intercalation compounds prepared in solutions of alkali metals in 2-methyltetrahydrofuran and 2,5-dimethyltetrahydrofuran

Abstract The intercalation of alkali metals (Li, K, Rb and Cs) into natural graphite flakes in the solutions of 2-methyltetrahydrofuran (MeTHF) and 2, 5-dimethyltetrahydrofuran (diMeTHF) containing naphthalene has been studied by X-ray diffraction (XRD), where naphthalene is used as a dissolving agent for alkali metals. When MeTHF is used as a solvent, binary Li- and K-graphite intercalation compounds (GICs) have been obtained, in contrast to the case of Rb and Cs, where both binary alkali metal GICs and ternary alkali metal-MeTHF-GICs are obtained. Using diMeTHF instead of MeTHF, a selective preparation of binary GICs for all the alkali metals has been established.

Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation

Abstract Electrochemical properties of graphite in propylene carbonate based electrolytes containing various organic solvents have been studied by cyclic voltammetry and charge–discharge measurements. Good correlation between solvent co-intercalation and electrochemical lithium intercalation into graphite was found. Effect of co-intercalated organic solvents in graphite on electrochemical Li intercalation was discussed.

Plasma etching of SiC surface using NF3

NF3 was applied in the reactive ion etching of SiC. The effects of rf power and NF3 pressure on the etching rate and the surface morphology were investigated by means of scanning electron microscopy and atomic force microscopy. A procedure for getting the smooth and residue-free etched surface of SiC with a high etching rate of 87 nm/min was obtained under the conditions such as rf power of 100 W and NF3 pressure ranging from 0.5 to 1 Pa. A rough surface with spikes was obtained under the NF3 pressures higher than 3 Pa. It was found that the repetitive alternating treatment for the spike-formed and rough surface with the down flow etching using NF3 and Ar plasma sputtering enables us to obtain the smooth surface within the scale of ∼300 nm.

Intercalation of lithium into natural graphite flakes and heat-treated polyimide films in ether-type solvents by chemical method

X-ray diffraction and Raman spectroscopy have been used to study the intercalation of Li into natural graphite flakes and heat-treated polyimide films (HTT = 1800–3000 °C) by chemical method in various ether-type solvents. Here, naphthalene was used as a dissolving agent for Li, and the solvents were tetrahydrofuran (THF), 2-methyltetrahydrofuran (MeTHF), 2,5-dimethyltetrahydrofuran (diMeTHF), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), 1-methoxypropane (MP), 1-methoxybutane (MB) and diethyl ether (Et2O). First, to elucidate the effects of the solvents, natural graphite flakes were used as a host material. By use of THF, DME and DEE, co-intercalation of Li and these solvents occurred to form ternary Li—solvent graphite intercalation compounds (GICs), but binary Li-GICs without solvents were obtained in MeTHF, diMeTHF, MP, MB and Et2O solvents. These results were confirmed by (00l) X-ray diffraction patterns. Second, co-intercalation of Li and THF into the heat-treated polyimide films was studied mainly by use of the Raman scattering results. As a result, co-intercalation of Li and THF occurred to form Li—THF—GIC for highly graphitized polyimide films heat-treated above 2400 °C, while only Li was found to be intercalated into the less graphitized films heat-treated below 2100 °C.

Up-to-date development of lithium-ion batteries in Japan

In this paper, the authors review the up-to-date development of lithium-ion batteries (LIBs), focusing mainly on the situation in Japan. The materials, constructions, and electrochemical performance of the latest commercially available LIBs, including lithium polymer batteries, which have come onto the market only fairly recently, are described in the first half of this article. The authors then discuss the recent trends in the development of battery materials for LIBs as well as those of large-scale LIBs.

Low temperature 7Li-NMR investigations on lithium inserted into carbon anodes for rechargeable lithium-ion cells

Abstract Lithium fully inserted into both graphitizable and non-graphitizable carbons has been investigated by 7 Li -NMR spectroscopy at low temperatures. It was found that lithium only in the non-graphitizable carbons heat-treated at ca. 1000°C showed peak separation phenomena at temperatures below −30°C. This peak separation is explained as exchange of lithium nuclei between different kinds of lithium species in the carbons. In addition, an equilibrium relationship between the lithium species in the non-graphitizable carbons was found in the temperature range from −30 to −150°C.